This invention relates to a digital-to-analog converter (D/A converter) consisting of capacitors for a weighted charge distribution corresponding to the digits of an n-digit binary number that is to be converted to analog form.
In systems for transmitting or processing information the input signals usually become available in analog form (pressure, temperature, voltage and so forth). An output signal in analog form is also mostly desired (control voltage). However, if the input signal is to be processed within a system in digital form for the purpose of excluding interference, then the input must include an analog-to-digital converter (A/D converter) and the output circuit a D/A converter. In view of the present requirement of large scale integration--the entire system being ideally integrated on a single semiconductor chip--it is essential for reasons of cost, power consumption and reliability to integrate these converters with the rest of the system. Only if this is done will the result be economically acceptable.
Three major considerations govern the design of networks integrated on a large scale:
The surface area needed for the implementation of the network should be a minimum.
The power consumption of the network should be a minimum.
The switching times should be as short as possible.
Particularly when D/A and A/D converters are incorporated in the integrated system the conversion time must match the signal processing time. The surface area required and the power consumption should generally be negligible compared with those of the remainder of the network. The surface area requirement should not exceed 10%. The principle disclosed in the published as-filed specification of German Patent Application Ser. No. 2,310,267 would not therefore be appropriate for the contemplated purpose.
In the case of a practicable effective semiconductor chip size of about 25 mm.sup.2 the capacitors of such a 10-bit D/A converter would already occupy 4 mm.sup.2. In other words, the D/A converter (transistors and capacitors) would take up 20% of the available overall surface.